Semiconductor Device Having Electrode and Manufacturing Method Thereof

ABSTRACT

A manufacturing method of a semiconductor device includes a first electrode formation step of forming a control gate electrode above a surface of a semiconductor substrate with a control gate insulating film interposed between the control gate electrode and the semiconductor substrate, a step of forming a storage node insulating film on the surface of the semiconductor substrate, and a second electrode formation step of forming a memory gate electrode on a surface of the storage node insulating film. The second electrode formation step includes a step of forming a memory gate electrode layer on the surface of the storage node insulating film, a step of forming an auxiliary film, having an etching rate slower than that of the memory gate electrode layer, on a surface of the memory gate electrode layer, and a step of performing anisotropic etching on the memory gate electrode layer and the auxiliary film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and amanufacturing method thereof.

2. Description of the Background Art

An example of a nonvolatile memory includes an EPROM (Erasable andProgrammable Read Only Memory) which is a ROM capable of electricallyrewriting data. An EPROM is generally classified into a UV-EPROM usingultraviolet rays for data erase and an EEPROM (Electrical Erasable andProgrammable Read Only Memory) electrically erasing data. An EEPROM doesnot erase data partially, but erases all pieces of data and, then,writes data to each memory cell.

An EEPROM can be mounted to a microcomputer for a mobile telephone, adigital home appliance or the like. For example, it is possible to forma semiconductor integrated circuit in which such an EEPROM and a CPU(Central Processing Unit) are formed on a surface of a chip.

An EEPROM includes an ONO (Oxide Nitride Oxide) film serving as a chargeaccumulation film for accumulating electrical charge in some cases. AnEEPROM has, for example, a MONOS (Metal Oxide Nitride OxideSemiconductor) structure using an ONO film or a SONOS (Silicon OxideNitride Oxide Semiconductor) structure. For example, data is written tosuch a nonvolatile memory when electrons are injected into an ONO film.In addition, data is erased from the nonvolatile memory when holes areinjected into the ONO film and, then, are recombined with theaccumulated electrons.

Japanese Patent Laying-Open No. 2003-309193 discloses a memory celltransistor having the following structure. That is, a pair of memoryelectrodes one of which is set at a source electrode and the other oneof which is set at a drain electrode mutually and a channel regioninterposed between the pair of memory electrodes are formed on a firstwell region. Further, a first gate electrode is provided near the memoryelectrode on the channel region with an insulating film interposedbetween the first gate electrode and the channel region. A second gateelectrode is also provided on the channel region with an insulating filmand a charge accumulation region each interposed between the second gateelectrode and the channel region, and is electrically isolated from thefirst gate electrode.

Japanese Patent Laying-Open No. 2003-100916 discloses a MONOS-typenonvolatile memory device in which a word gate, an impurity layer andsidewall-shaped first and second control gates are formed on a firstgate insulating film formed on a semiconductor substrate. Herein, eachof the first and second control gates has a rectangular sectional shape.

In Byung Yong Choi, et al., “Highly Scalable and Reliable 2-bit/cellSONOS Memory Transistor beyond 50 nm NVM Technology Using Outer SidewallSpacer Scheme with Damascene Gate Process”, IEEE 2005 Symposium on VLSITechnology Digest of Technical Papers, pp. 118-119, there is described atwo-bit/cell SONOS memory transistor beyond 50 nm NVM technology. In amethod for manufacturing such a memory transistor, first, an ONO film isformed on a surface of a semiconductor substrate. Then, in the ONO film,a portion corresponding to a substantially center of a channel isremoved; thus, two separated storage nodes are formed. This memoryexhibits high reliability even when being finely manufactured so as tohave a gate length of 80 nm.

Japanese Patent Laying-Open No. 2004-111629 discloses a manufacturingmethod of a MONOS memory. This manufacturing method includes: forming afirst gate insulating layer above a semiconductor substrate; forming afirst conductive layer word gate and a stopper layer; forming a firstinsulating layer and a second insulating layer on an entire memoryregion; performing anisotropic etching on the second insulating layer,thereby forming a first sidewall conductive layer; forming a thirdconductive layer on the entire memory region; performing anisotropicetching on the third conductive layer, thereby forming a second sidewallconductive layer; and performing isotropic etching on the first andsecond sidewall conductive layers, thereby forming a control gate.

Japanese Patent Laying-Open No. 11-145471 discloses a semiconductordevice in which an element isolation region is formed on a semiconductorsubstrate and a gate electrode is formed on the semiconductor substratewith a gate insulating film interposed between the gate electrode andthe semiconductor substrate. Herein, an insulating film having athickness “a” is formed on a top face of the gate electrode, and asidewall having a thickness “b” at a lowermost side is formed on a sideface of the gate electrode. The thickness of the sidewall at the heightof “a” from the top face of the gate electrode is not less than “b”,wherein “a”≧“b”.

A memory having a MONOS structure of a split gate type includes acontrol gate electrode of a control transistor and a memory gateelectrode of a MONOS transistor. The memory gate electrode is providedbeside the control gate electrode with an insulating film interposedbetween the memory gate electrode and the control gate electrode. An ONOfilm serving as a charge accumulation film is formed between the memorygate electrode and a semiconductor substrate.

In the memory having the MONOS structure of the split gate type, thememory gate electrode is formed as a sidewall of the control gateelectrode. More specifically, the control gate electrode is formed byphotolithography through a mask. On the other hand, the memory gateelectrode is formed by etching in a self aligned manner. The memory gateelectrode has an inclined top face in a sectional shape thereof. Inother words, the top face gradually becomes low in height toward anouter side. The memory gate electrode is high in height on a side nearthe control gate electrode and gradually becomes low in height toward anouter side.

In a step of forming a diffusion layer such as a source region or adrain region on a semiconductor substrate, ion implantation is performedin a self aligned manner while using the control gate electrode or thememory gate electrode as a mask. Since the outer side of the memory gateelectrode is low in height, ions implanted upon performance of the ionimplantation transmit through the memory gate electrode and, then, reachthe charge accumulation film in some cases. Consequently, there arises aproblem that the ONO film serving as the charge accumulation film isdegraded.

There is a design rule as a parameter indicating a level ofmicrofabrication. In a case that a manufacturable minimum dimension isset as such a design rule, recently, a semiconductor device ismanufactured below a 90 nm rule. In a photolithography step uponmanufacturing of a fine semiconductor device, an ArF light source isused as a light source for exposure, in place of a conventional KrFlight source. If the ArF light source is used, a fine circuit can beformed. However, it is necessary to make a portion to be exposed, suchas a resist, thin. If the resist is thin, a depth capable of performingetching becomes shallow in an etching step after development of theresist.

In a semiconductor device, for example, an interlayer insulating film isformed on a top face of a memory cell. The interlayer insulating film isformed for planarizing a surface and is provided on the top face of thememory cell. An interconnection is provided on the surface of theinterlayer insulating film, for example. In order to electricallyconnect between the interconnection and the memory cell, a contact isformed so as to pass through the interlayer insulating film. Uponformation of the contact, a through hole, which has a length equal to asum of a height of the memory cell and a height from a top of the memorycell to the surface of the interlayer insulating film, must be formed inthe interlayer insulating film.

In the semiconductor device in accordance with the design rule below a90 nm rule, however, the ArF light source is used for exposure.Therefore, there arises a problem that the resist becomes thin inthickness, so that a contact hole passing through the interlayerinsulating film cannot be formed in a step of forming a contact hole. Tothis end, there is required that a thickness of an interlayer insulatingfilm is made thin in a semiconductor device including a memory cell.

In order to prevent that ions are implanted into a charge accumulationfilm, it is considered that a height of a memory gate electrode is madehigh. However, if the height of the memory gate electrode is high, therearises a problem that a thickness of an interlayer insulating filmbecomes large. Alternatively, in order to prevent that ions areimplanted into a charge accumulation film, it is considered that energyof ions to be implanted is made small in an ion implantation step.However, the energy of the ions to be implanted is determined based onnecessity of countermeasures against shortcircuit failure between adiffusion layer and a substrate upon silicidation. Consequently, therearises a problem that it is impossible to make the energy of the ions tobe implanted small.

As a semiconductor circuit is formed finely, a gate electrode formed onan insulating film formed on a surface of a semiconductor substrate mustbe decreased in dimension. Consequently, there arises a problem thatdimensional accuracy becomes poor when the dimension of the gateelectrode is made small.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fine semiconductordevice and a manufacturing method thereof.

A manufacturing method of a semiconductor device according to one aspectof the present invention includes a first electrode formation step offorming a first electrode above a surface of a semiconductor substratewith a first insulating film interposed between the first electrode andthe semiconductor substrate, a charge accumulation film formation stepof forming a charge accumulation film beside the first electrode atleast on the surface of the semiconductor substrate, and a secondelectrode formation step of forming a second electrode on a surface ofthe charge accumulation film. Herein, the second electrode formationstep includes a step of forming a second electrode layer on the surfaceof the charge accumulation film, a step of forming an auxiliary film,having an etching rate slower than that of the second electrode layer,on a surface of the second electrode layer, and a step of performinganisotropic etching on the second electrode layer and the auxiliaryfilm, thereby forming the second electrode.

A manufacturing method of a semiconductor device according to anotheraspect of the present invention includes a step of forming a dummy filmhaving a side face on a surface of a semiconductor substrate, a step offorming a first insulating film on the surface of the semiconductorsubstrate, a step of forming a gate electrode layer on a surface of thefirst insulating film and a surface of the dummy film, a step of formingan auxiliary film, having an etching rate slower than that of the gateelectrode layer, on a surface of the gate electrode layer, a step ofperforming anisotropic etching on the gate electrode layer and theauxiliary film, thereby forming a gate electrode, a step of removing thedummy film, and a step of removing a portion corresponding to a regionoutside the gate electrode in the first insulating film.

A semiconductor device according to one aspect of the present inventionincludes a first electrode provided above a surface of a semiconductorsubstrate with a first insulating film interposed between the firstelectrode and the semiconductor substrate, a charge accumulation filmformed beside the first electrode on the surface of the semiconductorsubstrate, a second electrode provided on a surface of the chargeaccumulation film, and a sidewall insulating film provided beside thesecond electrode. Herein, the second electrode is formed such that asurface facing to the first electrode is substantially parallel with asurface facing to the sidewall insulating film in a sectional shapethereof. Further, the second electrode is formed such that a top face isrecessed in the sectional shape thereof.

A semiconductor device according to another aspect of the presentinvention includes a gate electrode provided above a surface of asemiconductor substrate with a first insulating film interposed betweenthe gate electrode and the semiconductor substrate, and sidewallinsulating films formed on both left and right sides of the gateelectrode in a sectional shape. Herein, the gate electrode is formedsuch that left and right surfaces facing to the sidewall insulatingfilms are substantially parallel with each other in the sectional shapethereof. Further, the gate electrode is formed such that a top face isrecessed in the sectional shape thereof.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first sectional view schematically illustrating asemiconductor device according to a first embodiment;

FIG. 2 is a second sectional view schematically illustrating thesemiconductor device according to the first embodiment;

FIG. 3 is a third sectional view schematically illustrating thesemiconductor device according to the first embodiment;

FIG. 4 is an enlarged sectional view schematically illustrating a memorycell in the first embodiment;

FIG. 5 is a circuit diagram illustrating the semiconductor deviceaccording to the first embodiment;

FIG. 6 is table showing a voltage applied for driving the semiconductordevice according to the first embodiment;

FIG. 7 illustrates a first step in a manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 8 illustrates a second step in the manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 9 is a first enlarged sectional view schematically illustrating acase of performing anisotropic etching in the manufacturing method ofthe semiconductor device according to the first embodiment;

FIG. 10 is a second enlarged sectional view schematically illustrating acase of performing anisotropic etching in the manufacturing method ofthe semiconductor device according to the first embodiment;

FIG. 11 illustrates a third step in the manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 12 illustrates a fourth step in the manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 13 illustrates a fifth step in the manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 14 illustrates a sixth step in the manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 15 illustrates a seventh step in the manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 16 illustrates an eighth step in the manufacturing method of thesemiconductor device according to the first embodiment;

FIG. 17 is an enlarged sectional view schematically illustrating acomparative example of the memory cell in the semiconductor deviceaccording to the first embodiment;

FIG. 18 is an enlarged sectional view schematically illustrating amemory cell in a semiconductor device according to a second embodiment;

FIG. 19 illustrates a first step in a manufacturing method of thesemiconductor device according to the second embodiment;

FIG. 20 illustrates a second step in the manufacturing method of thesemiconductor device according to the second embodiment;

FIG. 21 illustrates a third step in the manufacturing method of thesemiconductor device according to the second embodiment;

FIG. 22 illustrates a fourth step in the manufacturing method of thesemiconductor device according to the second embodiment;

FIG. 23 illustrates a fifth step in the manufacturing method of thesemiconductor device according to the second embodiment;

FIG. 24 illustrates a sixth step in the manufacturing method of thesemiconductor device according to the second embodiment;

FIG. 25 illustrates a seventh step in the manufacturing method of thesemiconductor device according to the second embodiment;

FIG. 26 is an enlarged sectional view schematically illustrating amemory cell in a semiconductor device according to a third embodiment;

FIG. 27 illustrates a first step in a manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 28 illustrates a second step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 29 illustrates a third step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 30 illustrates a fourth step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 31 illustrates a fifth step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 32 illustrates a sixth step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 33 illustrates a seventh step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 34 illustrates an eighth step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 35 illustrates a ninth step in the manufacturing method of thesemiconductor device according to the third embodiment;

FIG. 36 is an enlarged sectional view schematically illustrating asemiconductor device according to a fourth embodiment;

FIG. 37 illustrates a first step in a manufacturing method of thesemiconductor device according to the fourth embodiment;

FIG. 38 illustrates a second step in the manufacturing method of thesemiconductor device according to the fourth embodiment;

FIG. 39 illustrates a third step in the manufacturing method of thesemiconductor device according to the fourth embodiment;

FIG. 40 illustrates a fourth step in the manufacturing method of thesemiconductor device according to the fourth embodiment;

FIG. 41 illustrates a fifth step in the manufacturing method of thesemiconductor device according to the fourth embodiment;

FIG. 42 illustrates a sixth step in the manufacturing method of thesemiconductor device according to the fourth embodiment; and

FIG. 43 illustrates a seventh step in the manufacturing method of thesemiconductor device according to the fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Description will be given of a semiconductor device according to a firstembodiment of the present invention with reference to FIGS. 1 to 17. Thesemiconductor device according to this embodiment is an EEPROM, inparticular, a nonvolatile memory having an ONO film serving as a chargeaccumulation film.

FIG. 1 is a sectional view schematically illustrating the semiconductordevice according to this embodiment. FIG. 2 is a sectional view takenalong a line II-II in FIG. 1. FIG. 3 is a sectional view taken along aline III-III in FIG. 1.

With reference to FIG. 1, the semiconductor device according to thisembodiment includes control gate electrodes 5 and memory gate electrodes7. Control gate electrode 5 and memory gate electrode 7 are formed so asto extend substantially in parallel with each other when being seen in aplane. Control gate electrode 5 and memory gate electrode 7 are formedin a pair. In a surface of a semiconductor substrate, a diffusion layer12 a is formed on a region located between one pair of control gateelectrode 5 and memory gate electrode 7 and another pair of control gateelectrode 5 and memory gate electrode 7. Moreover, an interlayerinsulating film is formed on surfaces of control gate electrode 5 andmemory gate electrode 7. Interconnections 16 are formed on a surface ofthe interlayer insulating film. Interconnection 16 in this embodiment isformed so as to extend in a direction perpendicular to a direction inwhich control gate electrode 5 and memory gate electrode 7 extend. Onthe interlayer insulating film, contacts 15 are formed for achievingelectrical conduction from interconnections 16. Contact 15 is providedbeside a pair of control gate electrode 5 and memory gate electrode 7.

With reference to FIG. 2, a memory well portion 3 is formed on asemiconductor substrate 1. In this embodiment, a silicon substrate isused as semiconductor substrate 1. FIG. 2 illustrates two memory cells(elements).

A control gate electrode 5 serving as a first electrode is formed abovea surface of semiconductor substrate 1 with a control gate insulatingfilm 4 serving as a first insulating film interposed between controlgate electrode 5 and semiconductor substrate 1. A storage nodeinsulating film 6 serving as a charge accumulation film is formed on thesurface of semiconductor substrate 1, a side face of control gateelectrode 5 and a side face of control gate insulating film 4. A memorygate electrode 7 serving as a second electrode is formed on a surface ofstorage node insulating film 6. As described above, one pair of acontrol gate electrode and a memory gate electrode and another pair of acontrol gate electrode and a memory gate electrode are provided on bothsides of a contact 15 with insulating films interposed between the pairsand contact 15.

Sidewall insulating films 11 are formed on a side face of control gateelectrode 5 and a side face of memory gate electrode 7. A silicide film13 a is formed on a top face of control gate electrode 5 and a silicidefilm 13 b is formed on a top face of memory gate electrode 7. In thisembodiment, a CoSi film is used as each of silicide films 13 a and 13 b.

A protection insulating film 14 a is formed so as to surround controlgate electrode 5, memory gate electrode 7 and sidewall insulating films11. With regard to protection insulating film 14 a in this embodiment,an Si₃N₄ film which is a nitride film is formed as a self alignedcontact film.

An interlayer insulating film 14 b is provided on a surface ofprotection insulating film 14 a. Interlayer insulating film 14 b isformed so as to entirely cover the two memory cells. Interlayerinsulating film 14 b has a planarized surface.

Contact 15 is formed so as to pass through protection insulating film 14a and interlayer insulating film 14 b. Contact 15 includes conductivelayers 15 a and 15 b. Conductive layer 15 a is provided on a surface ofa contact hole formed in interlayer insulating film 14 b. Conductivelayer 15 b is provided inside conductive layer 15 a. An interconnection16 is formed on a surface of interlayer insulating film 14 b.Interconnection 16 includes metal layers 16 a to 16 c. Metal layer 16 ais electrically connected to contact 15.

On the surface of semiconductor substrate 1, an extension diffusionlayer 9 is formed at a source side and an extension diffusion layer 10is formed at a drain side. Impurities are injected into each ofextension diffusion layers 9 and 10. Extension diffusion layer 9 isformed so as to extend from a bottom side of memory gate electrode 7toward an outer side of the memory cell. Extension diffusion layer 10 isformed so as to extend from a bottom side of control gate electrode 5toward an outer side of the element.

Diffusion layers 12 a and 12 b each having impurities injected thereintoso as to be higher in concentration than that of each of extensiondiffusion layers 9 and 10 are formed on the surface of semiconductorsubstrate 1. Diffusion layer 12 a is formed so as to extend from aportion immediately below sidewall insulating film 11 provided on theside face of memory gate electrode 7 toward the outer side of the memorycell. Diffusion layer 12 b is formed immediately below contact 15.Diffusion layer 12 b is formed so as to extend from a bottom side ofsidewall insulating film 11 provided on the side face of control gateelectrode 5 toward the outer side of the memory cell. Diffusion layer 12b is formed so as to crosslink between the two memory cells. At asubstantially center portion in a direction in which diffusion layers 12a and 12 b extend, a silicide film 13 c is formed for reducingelectrical resistance. In this embodiment, a CoSi film is used assilicide film 13 c. Contact 15 is electrically connected to silicidefilm 13 c.

With reference to FIG. 3, an element isolation portion 2 is formed onmemory well portion 3. Interlayer insulating film 14 b has theplanarized surface. Interconnections 16 in this embodiment are formed soas to extend in parallel with each other. Interconnection 16 is formedsuch that a sectional shape when being cut in a direction perpendicularto an extending direction is rectangular.

FIG. 4 is an enlarged sectional view schematically illustrating thememory cell as the element in this embodiment. In this embodiment,control gate insulating film 4 is formed on the surface of semiconductorsubstrate 1. Control gate electrode 5 is formed on the surface ofcontrol gate insulating film 4. In this embodiment, control gateelectrode 5 is formed so as to have a rectangular sectional shape.Control gate electrode 5 is provided above the surface of thesemiconductor substrate 1 with control gate insulating film 4 interposedbetween control gate electrode 5 and semiconductor substrate 1.

In this embodiment, storage node insulating film 6 serving as a chargeaccumulation film is an ONO film. Storage node insulating film 6includes silicon oxide films 6 a and 6 c and an silicon nitride film 6b. Storage node insulating film 6 is provided on the surface ofsemiconductor substrate 1, one of the side faces of control gateelectrode 5 and one of the side faces of control gate insulating film 4.Storage node insulating film 6 is formed so as to have an “L”-shapedsectional shape. Storage node insulating film 6 includes a portioninterposed between semiconductor substrate 1 and memory gate electrode7.

Sidewall insulating film 11 is formed on the other one of the side facesof control gate electrode 5 and the other one of the side faces ofcontrol gate insulating film 4. Sidewall insulating film 11 is formed onthe side face of memory gate electrode 7 and a side face of storage nodeinsulating film 6.

Memory gate electrode 7 is formed such that a surface facing to controlgate electrode 5 is substantially parallel with a surface facing tosidewall insulating film 11 in a sectional shape thereof. Morespecifically, in this embodiment, memory gate electrode 7 is formed suchthat a width is substantially constant in a height direction in thesectional shape thereof.

Memory gate electrode 7 is formed such that a substantially centerportion of a top face is recessed in a width direction in the sectionalshape thereof. Memory gate electrode 7 is formed so as to have a sectionin a direction perpendicular to an extending direction such that acenter portion of a top face is recessed. Memory gate electrode 7 isformed such that the top face is formed into a substantially “V” shapein the sectional shape thereof.

In a height of memory gate electrode 7, it is assumed herein that amaximum height is Hmg_H and a minimum height is Hmg_L. In a case thatimpurities are injected into semiconductor substrate 1 in an ionimplantation step of forming diffusion layer 12 a in a manufacturingprocess, minimum height Hmg_L is set such that the impurities areprevented from reaching storage node insulating film 6. In other words,in the ion implantation step of forming diffusion layer 12 a, memorygate electrode 7 has a sufficient height such that impurities areprevented from reaching storage node insulating film 6.

The semiconductor device according to this embodiment has a smalldifference between maximum height Hmg_H and minimum height Hmg_L;therefore, maximum height Hmg_H can be made low. In other words, theheight of memory gate electrode 7 can be made low, and the height of theinterlayer insulating film provided on the memory cell can be made lowas a whole. In FIG. 2, a height Hi of interlayer insulating film 14 bcan be made low. As a result, a depth of a contact hole for formingcontact 15 can be made shallow. For example, even in a finesemiconductor device below a 90 nm rule, a contact hole can be formedwith high reliability.

FIG. 5 is a circuit diagram illustrating the semiconductor deviceaccording to this embodiment. FIG. 6 is a table showing a voltageapplied for driving the semiconductor device according to thisembodiment.

In FIG. 5, “MG1” to “MG4” denote lines of memory gate electrode 7. “CG1”to “CG4” denote lines of control gate electrode 5. “BL1” and “BL2”denote interconnections 16 formed on the surface of the interlayerinsulating film (see FIGS. 1 to 3). “SL1” and “SL2” denote diffusionlayers 12 a. A region 61 denotes a portion including memory gateelectrode 7 and storage node insulating film 6. A region 62 denotes aportion including control gate electrode 5 and control gate insulatingfilm 4.

With reference to FIG. 6, operations of the semiconductor deviceaccording to this embodiment include a read operation, a write operationand an erase operation. In FIG. 6, “Vmg” denotes a voltage of a memorygate electrode, “Vs” denotes a voltage of a diffusion layer at a sourceside, “Vcg” denotes a voltage of a control gate electrode, and “Vd”denotes a voltage of a diffusion layer at a drain side. Also in FIG. 6,“Vsub” denotes a voltage of a semiconductor substrate.

In the write operation of the semiconductor device according to thisembodiment, a positive voltage is applied to a memory gate electrode anda diffusion layer at a source side, respectively, by source-sideinjection. A small positive voltage is applied to a control gateelectrode. Electrons travel toward the source side along a main surfaceof semiconductor substrate 1. When the electrons collide with anextension diffusion layer at the source side, hot electrons aregenerated. The generated hot electrons are attracted to the voltage ofthe control gate electrode and are accumulated on an silicon nitridefilm in a storage node insulating film.

In the erase operation of the semiconductor device according to thisembodiment, hot hole injection by an interband tunnel is adopted. Anegative voltage is applied to a memory gate electrode. A positiveelectrode, that is, a reverse bias, is applied to a diffusion layer at asource side. A strong electric field at an end of an extension diffusionlayer at the source side generates hot holes by an interband tunnel. Thehot holes are injected into an silicon nitride film of a storage nodeinsulating film and, then, are coupled to electrons; thus, the electronsare erased.

In the read operation of the semiconductor device according to thisembodiment, a positive voltage is applied to a memory gate electrode anda control gate electrode, respectively. Further, a positive voltage isapplied to a diffusion layer at a drain side. Herein, it is determinedwhether or not is information is recorded, based on magnitude of acurrent flowing into the diffusion layer at the drain side.

Next, description will be given of a manufacturing method of thesemiconductor device according to this embodiment with reference toFIGS. 7 to 16.

FIG. 7 is a sectional view schematically illustrating a first step inthe manufacturing method of the semiconductor device according to thisembodiment. First, ions are implanted into a surface of a semiconductorsubstrate 1, so that a memory well portion 3 is formed.

Next, a first electrode formation step is carried out for forming afirst electrode above the surface of the semiconductor substrate with afirst insulating film interposed between the first electrode and thesemiconductor substrate. For example, a thermal oxidation film is formedas a layer corresponding to a control gate insulating film 4 on thesurface of semiconductor substrate 1. Further, a polysilicon layer isformed as a layer corresponding to a control gate electrode 5 on asurface of the layer corresponding to control gate insulating film 4.Thereafter, patterning is performed by photolithography, so that controlgate insulating film 4 is formed as a first insulating film. Inaddition, control gate electrode 5 is formed as the first electrodehaving a substantially square sectional shape.

FIG. 8 is a sectional view schematically illustrating a second step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a charge accumulation film formation step is carriedout for forming a charge accumulation film. A storage node insulatingfilm 6 serving as a charge accumulation film is formed on the surface ofsemiconductor substrate 1, a side face of control gate insulating film 4and a surface of control gate electrode 5. Storage node insulating film6 is formed on at least a portion beside control gate electrode 5 on thesurface of semiconductor substrate 1. In this embodiment, an ONO filmincluding three layers: an SiO₂ film, an Si₃N₄ film and an SiO₂ film isused as storage node insulating film 6 (see FIG. 4).

Next, a second electrode formation step is carried out for forming amemory gate electrode serving as a second electrode on a surface of thecharge accumulation film. A memory gate electrode layer 7 a serving as asecond electrode layer is provided on the surface of storage nodeinsulating film 6. The second electrode layer is formed so as to coverstorage node insulating film 6. In this embodiment, an amorphous siliconfilm doped with impurities is laminated as memory gate electrode layer 7a.

Next, an auxiliary film 8 is formed on a surface of memory gateelectrode layer 7 a. Auxiliary film 8 is slower in a rate of etchingperformed in a later step than that of memory gate electrode layer 7 a.In this embodiment, a silicon oxide film is formed as auxiliary film 8.The silicon oxide film can be formed in such a manner that the surfaceof memory gate electrode layer 7 a is subjected to thermal oxidation.This thermal oxidation of the surface of memory gate electrode layer 7 afacilitates control of auxiliary film 8 in thickness. The method offorming the silicon oxide film is not limited to the aforementionedmethod. The silicon oxide film may be formed in such a manner that ansilicon oxide film is laminated on the surface of memory gate electrodelayer 7 a.

An auxiliary film is not limited to the aforementioned auxiliary film aslong as it has an etching rate slower than that of a memory gateelectrode layer in anisotropic etching performed in a later step. Inthis embodiment, for example, a nitride film may be formed as theauxiliary film.

Preferably, the auxiliary film is a film having a selectivity ratiobetween memory gate electrode layer 7 a and auxiliary film 8 ofsubstantially 10:1, in consideration of optimal etching in a later stepof performing anisotropic etching.

Next, anisotropic etching is performed as shown by an arrow 51. Inauxiliary film 8, a portion provided substantially in a horizontaldirection is preferentially subjected to etching.

FIG. 9 is an enlarged sectional view schematically illustrating an upperportion of a control gate electrode subjected to anisotropic etching. Byperformance of the anisotropic etching, first, the portion extending inthe horizontal direction is removed in auxiliary film 8, so that memorygate electrode layer 7 a is subjected to etching. At a top side ofcontrol gate electrode 5, an upper portion of memory gate electrodelayer 7 a is subjected to etching.

FIG. 10 is an enlarged sectional view schematically illustrating theupper portion of the control gate electrode further subjected toanisotropic etching continuously. Since an etching rate of auxiliaryfilm 8 is slower than that of memory gate electrode layer 7 a, memorygate electrode layer 7 a is preferentially removed. More specifically,since the etching rate of auxiliary film 8 is slow, most of auxiliaryfilm 8 is remained and most of memory gate electrode layer 7 a isremoved. Memory gate electrode layer 7 a is subjected to etching at aportion away from auxiliary film 8 rather than a portion near auxiliaryfilm 8. The anisotropic etching is continuously performed until memorygate electrode layer 7 a provided on control gate electrode 5 isremoved.

FIG. 11 is a sectional view schematically illustrating a third step inthe manufacturing method of the semiconductor device according to thisembodiment. FIG. 11 is a sectional view schematically illustrating astate after completion of anisotropic etching. Memory gate electrodelayer 7 a is partially removed; thus, a memory gate electrode 7 isformed. Memory gate electrode 7 is formed such that a thickness in awidth direction becomes substantially constant in a height direction. Atop face of memory gate electrode 7 is formed such that a substantiallycenter portion of memory gate electrode 7 is recessed in a widthdirection. In this embodiment, the top face of memory gate electrode 7is formed into a substantially “V” shape. Auxiliary film 8 is partiallyremained on a side face of memory gate electrode 7.

FIG. 12 is a sectional view schematically illustrating a fourth step inthe manufacturing method of the semiconductor device according to thisembodiment. By performance of isotropic etching such as wet etching,auxiliary film 8 remained on the side face of memory gate electrode 7 isremoved.

FIG. 13 is a sectional view schematically illustrating a fifth step inthe manufacturing method of the semiconductor device according to thisembodiment. One of memory gate electrodes 7 provided on the both sidesof control gate electrode 5 is removed. In this embodiment, a mask isprovided on the surface of control gate electrode 5 by photolithographyto remove one of memory gate electrodes 7. Further, isotropic etchingsuch as wet etching is performed for removing a portion other than aportion interposed between memory gate electrode 7 and control gateelectrode 5 and a portion interposed between semiconductor substrate 1and memory gate electrode 7 in storage node insulating film 6. Storagenode insulating film 6 is formed so as to have an “L”-shaped sectionalshape.

FIG. 14 is a sectional view schematically illustrating a sixth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, ions are implanted into semiconductor substrate 1 in aself aligned manner while using each of control gate electrode 5 andmemory gate electrode 7 as a mask. By performance of this ionimplantation, an extension diffusion layer 9 at a source side and anextension diffusion layer 10 at a drain side are formed. With regard tothis ion implantation, for example, arsenic is implanted at 2×10¹⁵atoms/cm² with an energy of 5 kev.

FIG. 15 is a sectional view schematically illustrating a seventh step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, sidewall insulating films 11 are formed on the sideface of control gate electrode 5 and the side face of memory gateelectrode 7.

Next, as shown by an arrow 52, ions are implanted into semiconductorsubstrate 1 in a self aligned manner while using each of control gateelectrode 5, memory gate electrode 7 and sidewall insulating film 11 asa mask. By performance of this ion implantation, a diffusion layer 12 aat the source side and a diffusion layer 12 b at the drain side areformed. With regard to this ion implantation, for example, arsenic isinjected at 2×10¹⁵ atoms/cm² with an energy of 50 kev and phosphorus isinjected at 1×10¹³ atoms/cm² with an energy of 40 kev.

In the manufacturing method of the semiconductor device according tothis embodiment, a minimum height of memory gate electrode 7 is high ina width direction upon implantation of ions with high energy. Therefore,it is possible to suppress that implanted ions transmit through memorygate electrode 7 to reach the portion interposed between semiconductorsubstrate 1 and memory gate electrode 7 in storage node insulating film6.

FIG. 16 is a sectional view schematically illustrating an eighth step inthe manufacturing method of the semiconductor device according to thisembodiment. Silicide films 13 c are formed on surfaces of diffusionlayers 12 a and 12 b on semiconductor substrate 1. Upon formation ofsilicide film 13 c, for example, a cobalt film is deposited on the mainsurface of semiconductor substrate 1 and, then, cobalt is reacted withsilicon by heat treatment. Thereafter, when the cobalt film is removed,a silicide film can be formed. Silicide film 13 c is formed on the mainsurface of semiconductor substrate 1 and, concurrently, a silicide film13 a is formed on the top face of control gate electrode 5 and asilicide film 13 b is formed on the top face of memory gate electrode 7.

With reference to FIG. 2, next, a protection insulating film 14 a isformed so as to cover control gate electrode 5, memory gate electrode 7and sidewall insulating film 11. In this embodiment, an Si₃N₄ film isformed as protection insulating film 14 a.

Next, an interlayer insulating film 14 b is provided on a surface ofprotection insulating film 14 a. Next, for example, a resist is providedonto a surface of interlayer insulating film 14 b to perform patterningfor forming a contact hole by photolithography. Next, a contact hole isformed in interlayer insulating film 14 b by etching. In thisembodiment, a height of a memory cell can be made low; therefore, anentire thickness Hi of interlayer insulating film 14 b can be madesmall. Accordingly, in a step of forming a semiconductor circuit inaccordance with a 90 nm rule, for example, an ArF light source is usedas a light source for exposure of a resist. Even when the resist is thinin the surface of interlayer insulating film 14 b, a contact holepassing through the interlayer insulating film can be formed securely.

Conductive layers 15 a and 15 b are laminated on a surface of the formedcontact hole; thus, a contact 15 is formed. Next, a surface ofinterlayer insulating film 14 b is planarized by, for example, CMP(Chemical Mechanical Polishing). Next, an interconnection 16 includingmetal layers 16 a to 16 c is formed on the surface of the interlayerinsulating film 14 b.

The semiconductor device according to this embodiment can bemanufactured as described above. The manufacturing method of thesemiconductor device according to this embodiment includes a secondelectrode formation step of forming a memory gate electrode serving as asecond electrode. The second electrode formation step includes a step offorming an auxiliary film having an etching rate slower than that of amemory gate electrode, and a step of performing anisotropic etching onthe second electrode layer and the auxiliary film. According to thismethod, a substantially center portion of a top face of the memory gateelectrode can be recessed; thus, a memory cell to be formed can be madelow in height.

FIG. 17 is a sectional view schematically illustrating a comparativeexample of the semiconductor device according to this embodiment. Thesemiconductor device in the comparative example is manufactured asfollows. That is, in the second electrode formation step in thisembodiment, no auxiliary film is formed on the surface of the secondelectrode layer.

In a step of performing anisotropic etching for forming a memory gateelectrode 41 (see FIG. 8), a top face of memory gate electrode 41 isremoved at an outer side thereof frequently rather than an inner sidethereof. As a result, memory gate electrode 41 has a sectional shape inwhich the top plane face is inclined.

As for the semiconductor device in the comparative example, memory gateelectrode 41 has a large difference between a maximum height Hmg_H and aminimum height Hmg_L. Herein, in a case that the height of memory gateelectrode 41 is made low in order to finely manufacture thesemiconductor device, minimum height Hmg_L becomes disadvantageouslylow, so that ions to be implanted reach storage node insulating film 6in a later ion implantation step of forming a diffusion layer. Hence, itis difficult to finely manufacture the semiconductor device.

In this embodiment, however, a difference between a minimum height and amaximum height in a memory gate electrode can be made small, and themaximum height of the memory gate electrode can be made low. As aresult, a thickness of an interlayer insulating film can be made thin,so that a contact hole can be formed securely. That is, a semiconductordevice can be manufactured finely in this embodiment.

In the manufacturing method of the semiconductor device according tothis embodiment, further, an auxiliary film is remained on a side faceof a memory gate electrode in a second electrode formation step.Therefore, it is possible to prevent etching from being performed on thememory gate electrode in a width direction, and to form a memory gateelectrode excellent in dimensional accuracy in a width direction.Accordingly, it is possible to manufacture a semiconductor device havinga memory gate electrode small in width.

In this embodiment, as described above, it is possible to manufacture afine semiconductor device or to make an allowance (process margin) uponmanufacturing of a semiconductor device large.

The present invention is not only applicable to a memory cell having aMONOS structure, but also applicable to a memory cell having a SONOSstructure.

Second Embodiment

Description will be given of a semiconductor device according to asecond embodiment of the present invention with reference to FIGS. 18 to25. The semiconductor device according to this embodiment is a so-calledtwo-bit/cell nonvolatile memory in which memory gate electrodes areformed on both sides of a control gate electrode.

FIG. 18 is a sectional view schematically illustrating the semiconductordevice according to this embodiment. The semiconductor device accordingto this embodiment includes a control gate electrode 5 serving as afirst electrode and memory gate electrodes 7 each serving as a secondelectrode. Herein, memory gate electrodes 7 are formed on both sides ofcontrol gate electrode 5.

An extension diffusion layer 9 and a diffusion layer 12 a are formed ona surface of a semiconductor substrate 1. Extension diffusion layer 9 isformed so as to extend from a bottom side of memory gate electrode 7toward an outer side of a memory cell. Control gate electrode 5 isprovided above the surface of semiconductor substrate 1 with a controlgate insulating film 4 serving as a first insulating film interposedbetween control gate electrode 5 and semiconductor substrate 1.

Storage node insulating films 6 each serving as a charge accumulationfilm are formed so as to extend from a side face of control gateelectrode 5 toward a top face of semiconductor substrate 1. In thisembodiment, storage node insulating film 6 is formed so as to have an“L”-shaped sectional shape. Herein, storage node insulating films 6 areformed on the both sides of control gate electrode 5.

Memory gate electrode 7 is formed on a surface of storage nodeinsulating film 6. Storage node insulating film 6 is interposed betweenmemory gate electrode 7 and semiconductor substrate 1. Storage nodeinsulating film 6 is interposed between memory gate electrode 7 andcontrol gate electrode 5. Each memory gate electrode 7 is formed suchthat a surface facing to control gate electrode 5 is substantiallyparallel with a surface facing to a sidewall insulating film 11. Memorygate electrode 7 is formed such that a width is substantially constantin a height direction in a sectional shape thereof. Each memory gateelectrode 7 is formed so as to have a top face in which a center portionis recessed in a width direction.

Description will be given of a manufacturing method of the semiconductordevice according to this embodiment with reference to FIGS. 19 to 25.

FIG. 19 is a sectional view schematically illustrating a first step inthe manufacturing method of the semiconductor device according to thisembodiment. First, a memory well portion 3 is formed on a semiconductorsubstrate 1. Next, a first electrode formation step is carried out forforming a first electrode above a surface of semiconductor substrate 1.More specifically, a control gate insulating film 4 serving as a firstinsulating film and a control gate electrode 5 serving as a firstelectrode are formed on the surface of semiconductor substrate 1.

FIG. 20 is a sectional view schematically illustrating a second step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a storage node insulating film 6 serving as a chargeaccumulation film is formed so as to cover the surface of semiconductorsubstrate 1 and a surface of control gate electrode 5. For example, anONO film is formed as storage node insulating film 6.

Next, a second electrode formation step is carried out for forming asecond electrode. A memory gate electrode layer 7 a serving as a secondelectrode layer is formed on a surface of storage node insulating film6. An auxiliary film 8 is formed on a surface of memory gate electrodelayer 7 a. Auxiliary film 8 formed herein has an etching rate slowerthan that of memory gate electrode layer 7 a in a later etching step.

Next, anisotropic etching is performed as shown by an arrow 53. Inauxiliary film 8, a portion extending in the horizontal direction isremoved by performance of the anisotropic etching. Next, memory gateelectrode layer 7 a is removed partially.

FIG. 21 is a sectional view schematically illustrating a third step inthe manufacturing method of the semiconductor device according thisembodiment. More specifically, FIG. 21 illustrates a state aftercompletion of anisotropic etching. Memory gate electrodes 7 each havinga substantially square sectional shape are formed on both sides ofcontrol gate electrode 5. Each memory gate electrode 7 is formed so asto have a top face in which a substantially center portion is recessedin a width direction. Also in this embodiment, as described above,auxiliary film 8 is formed on the surface of memory gate electrode 7 a.Thus, it is possible to prevent that the top face of memory gateelectrode 7 becomes low toward an outer side.

FIG. 22 is a sectional view schematically illustrating a fourth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, auxiliary film 8 remained on the side face of memorygate electrode 7, is removed by wet etching. Further, in storage nodeinsulating film 6, a portion other than a portion interposed betweencontrol gate electrode 5 and memory gate electrode 7 and a portioninterposed between semiconductor substrate 1 and memory gate electrode 7is removed by anisotropic etching.

FIG. 23 is a sectional view schematically illustrating a fifth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, ion implantation is performed in a self aligned mannerwhile using each of control gate electrode 5 and memory gate electrode 7as a mask, so that an extension diffusion layer 9 is formed.

FIG. 24 is a sectional view schematically illustrating a sixth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a sidewall insulating film 11 is formed. Next, asshown by an arrow 54, ion implantation is performed, so that a diffusionlayer 12 is formed. Herein, ions with high energy are implanted intosemiconductor substrate 1. Memory gate electrode 7 has a sufficientlyhigh minimum height; therefore, it is possible to prevent that ions tobe implanted transmit through memory gate electrode 7 to reach storagenode insulating film 6.

FIG. 25 is a sectional view schematically illustrating a seventh step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, in the surface of semiconductor substrate 1, asilicide film 13 c is formed on a bared portion. Concurrently with theformation of silicide film 13 c, a silicide film 13 a is formed on a topface of control gate electrode 5 and a silicide film 13 b is formed on atop face of memory gate electrode 7.

Thereafter, a protection insulating film is formed so as to cover acell. Further, an interlayer insulating film is provided on a surface ofthe protection insulating film, and a contact hole is formed in theinterlayer insulating film. Then, a contact is formed in the contacthole.

The manufacturing method of the semiconductor device according to thisembodiment has the following advantage. That is, in a second electrodeformation step of forming a second electrode, anisotropic etching isperformed in such a manner that an auxiliary film having an etching rateslower than that of a second electrode layer is formed on a surface ofthe second electrode layer; therefore, a memory gate electrode can havea top face in which a center portion is recessed in a width direction.Thus, it is possible to make a difference between a minimum height and amaximum height of the memory gate electrode small, and to make themaximum height of the memory gate electrode low. As a result, it ispossible to finely manufacture a semiconductor device. In addition, itis possible to provide a semiconductor device which is improved incontrollability of a length of a width of a memory gate electrode and issmall in a width direction.

The other configurations, actions, effects and manufacturing processesare similar to those in the first embodiment; therefore, specificdescription thereof will not be repeated here.

Third Embodiment

Description will be given of a semiconductor device according to a thirdembodiment of the present invention with reference to FIGS. 26 to 35.The semiconductor device according to this embodiment is a nonvolatilememory in which a charge accumulation film is formed on a surface of asemiconductor substrate and no charge accumulation film is formed on aside face of a control gate electrode.

FIG. 26 is a sectional view schematically illustrating the semiconductordevice according to this embodiment. In the semiconductor deviceaccording this embodiment, a control gate electrode 22 is formed above asurface of a semiconductor substrate 17 with a control gate insulatingfilm 21 serving as a first insulating film interposed between controlgate electrode 22 and semiconductor substrate 17. Control gate electrode22 is formed so as to have a square sectional shape. Control gateinsulating film 21 is interposed between control gate electrode 22 andsemiconductor substrate 17 and between control gate electrode 22 andmemory gate electrode 24. Control gate insulating film 21 is formed on abottom face and side faces of control gate electrode 22.

A storage node insulating film 19 is formed beside control gateelectrode 22 on the surface of semiconductor substrate 17. Storage nodeinsulating film 19 is interposed between semiconductor substrate 17 andmemory gate electrode 24. Storage node insulating film 19 includessilicon oxide films 19 a and 19 c and an silicon nitride film 19 b.

A memory gate electrode 24 is formed on a top face of storage nodeinsulating film 19. Memory gate electrode 24 is formed so as to have asubstantially square sectional shape. Memory gate electrode 24 is formedsuch that a surface facing to control gate electrode 22 is substantiallyparallel with a surface facing to a sidewall insulating film 27. Memorygate electrode 24 is formed such that a width becomes substantiallyconstant in a height direction in a sectional shape thereof. Memory gateelectrode 24 is formed so as to have a top face in which a substantiallycenter portion is recessed in a width direction.

A silicide film 29 a is formed on a top face of control gate electrode22. A silicide film 29 b is formed on a top face of a memory gateelectrode 24. An extension diffusion layer 26 is formed on the surfaceof semiconductor substrate 17 so as to extend from a bottom side ofmemory gate electrode 24 toward an outer side of a memory cell.

Sidewall insulating film 27 is formed on a side face of memory gateelectrode 24 and a side face of storage node insulating film 19. Adiffusion layer 28 is formed on the surface of semiconductor substrate17 so as to extend from a bottom side of sidewall insulating film 27toward the outer side of the memory cell. A silicide film 29 c is formedbeside sidewall insulating film 27 on the surface of semiconductorsubstrate 17.

Description will be given of a manufacturing method of the semiconductordevice according to this embodiment with reference to FIGS. 27 to 34.

FIG. 27 is a sectional view schematically illustrating a first step inthe manufacturing method of the semiconductor device according to thisembodiment. First, a first electrode formation step is carried out forforming a control gate electrode serving as a first electrode. A memorywell portion 18 is formed on a surface of a semiconductor substrate 17.Next, a storage node insulating film 19 and a dummy layer 20 are formedon the surface of semiconductor substrate 17. For example, a laminationof an silicon oxide film, an silicon nitride film and an silicon oxidefilm is used as storage node insulating film 19, and an silicon nitridefilm is used as dummy layer 20.

Next, an opening 20 a is formed in dummy layer 20 and storage nodeinsulating film 19 by photolithography. Opening 20 a is formed so as toreach the surface of semiconductor substrate 17.

FIG. 28 is a sectional view schematically illustrating a second step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a control gate insulating film 21 is formed on asurface of dummy layer 20 including opening 20 a and a surface ofsemiconductor substrate 17 having opening 20 a formed therein. Forexample, an silicon oxide film is used as control gate insulating film21. Next, a control gate electrode layer 22 a serving as a control gateelectrode is formed on a surface of control gate insulating film 21.Control gate electrode layer 22 a is formed such that opening 20 a isfilled therewith.

FIG. 29 is a sectional view schematically illustrating a third step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, in control gate electrode layer 22 a, a portion higherin height than dummy layer 20 and a portion corresponding to controlgate insulating film 21 formed on a top face of dummy layer 20 areremoved by, for example, chemical mechanical polishing. In other words,portions higher in height than opening 20 a are removed in control gateinsulating film 21 and control gate electrode layer 22 a. By thisremoval step, a control gate electrode 22 serving as a first electrodeis formed. A control gate insulating film 21 serving as a firstinsulating film is formed on a bottom face and a side face of controlgate electrode 22.

FIG. 30 is a sectional view schematically illustrating a fourth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a control gate protection film 23 serving as a secondinsulating film is formed on a top face of control gate electrode 22 byphotolithography. Next, dummy layers 20 provided on both sides ofcontrol gate insulating film 21 are removed.

FIG. 31 is a sectional view schematically illustrating a fifth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a memory gate electrode layer 24 a serving as a secondelectrode layer is formed on a surface of storage node insulating film19, a surface of control gate insulating film 21 and a surface ofcontrol gate protection film 23. Further, an auxiliary film 25 is formedon a surface of memory gate electrode layer 24 a. Auxiliary film 25formed herein has an etching rate slower than that of memory gateelectrode layer 24 a in a later etching step. Next, anisotropic etchingis performed as shown by an arrow 55.

FIG. 32 is a sectional view schematically illustrating a sixth step inthe manufacturing method of the semiconductor device according to thisembodiment. More specifically, FIG. 32 illustrates a state aftercompletion of anisotropic etching. Memory gate electrodes 24 are formedon both sides of control gate electrode 22 with control gate insulatingfilm 21 interposed between each memory gate electrode 24 and controlgate electrode 22. Memory gate electrode 24 has a top face in which asubstantially center portion is recessed in a width direction. Auxiliaryfilm 25 is partially remained on the side face of memory gate electrode24.

FIG. 33 is a sectional view schematically illustrating a seventh step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, remained auxiliary film 25 is removed by etching.Further, in storage node insulating film 19, a bared portion is removedby etching. Storage node insulating film 19 is remained on a regioninterposed between memory gate electrode 24 and semiconductor substrate17. Next, ion implantation is performed to form an extension diffusionlayer 26.

FIG. 34 is a sectional view schematically illustrating an eighth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a sidewall insulating film 27 is formed on a side faceof memory gate electrode 24 and a side face of storage node insulatingfilm 19. Next, as shown by an arrow 56, a diffusion layer 28 is formedin a self aligned manner. Also in an ion implantation step of formingdiffusion layer 28, memory gate electrode 24 has a sufficient highminimum height. Therefore, it is possible to prevent that ions transmitthrough memory gate electrode 24 to reach storage node insulating film19.

FIG. 35 is a sectional view schematically illustrating a ninth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a silicide film 29 c is formed on the surface ofsemiconductor substrate 17. Herein, a silicide film 29 a is formed on atop face of control gate electrode 22 and a silicide film 29 b is formedon a top face of memory gate electrode 24.

Also by the manufacturing method of the semiconductor device accordingto this embodiment, it is possible to manufacture a fine semiconductordevice.

The other configurations, actions, effects and manufacturing processesare similar to those in the first and second embodiments; therefore,specific description thereof will not be repeated.

Fourth Embodiment

Description will be given of a semiconductor device according to afourth embodiment of the present invention with reference to FIGS. 36 to43. The semiconductor device in this embodiment is a MOS (Metal OxideSemiconductor) transistor.

FIG. 36 is a sectional view schematically illustrating the semiconductordevice according to this embodiment. A gate electrode 34 is formed abovea surface of a semiconductor substrate 31 with a gate insulating film 33interposed between gate electrode 34 and semiconductor substrate 31.Sidewall insulating films 37 are formed on side faces of gate electrode34.

Extension diffusion layers 36 are formed on the surface of semiconductorsubstrate 31 so as to extend from a bottom side of gate electrode 34toward an outer side. Extension diffusion layers 36 are formed on bothsides of semiconductor substrate 31 in a width direction. In addition,diffusion layers 38 are formed on the surface of semiconductor substrate31 so as to extend from a bottom side of sidewall insulating film 37toward the outer side. A silicide film 39 b is formed beside eachsidewall insulating film 37 on the surface of semiconductor substrate31.

Gate electrode 34 is formed such that surfaces facing to sidewallinsulating films 37 are substantially parallel with each other in asectional shape thereof. Gate electrode 34 is formed so as to have asubstantially square sectional shape. Gate electrode 34 is formed suchthat a substantially center portion of a top face is recessed in a widthdirection in the sectional shape thereof. In this embodiment, the topface of gate electrode 34 has a substantially “V”-shaped sectionalshape. A silicide film 39 a is formed on the top face of gate electrode34.

The semiconductor device according to this embodiment is excellent indimensional accuracy of a width of gate electrode 34. As a result, it ispossible to provide a fine semiconductor device having a gate electrodesmall in width. The improvement in dimensional accuracy of the gateelectrode improves dimensional accuracy of a diffusion layer and, also,improves a process margin upon formation of the diffusion layer.Further, when ions are implanted in a step of forming the diffusionlayer, it is possible to prevent that the ions transmit through a gateelectrode to reach a gate insulating film. As a result, it is possibleto suppress a change in transistor characteristics due to implantationof ions into the gate insulating film.

Description will be given of a manufacturing method of the semiconductordevice according to this embodiment with reference to FIGS. 37 to 43.

FIG. 37 is a sectional view schematically illustrating a first step inthe manufacturing method of the semiconductor device according to thisembodiment. As illustrated in FIG. 37, first, a well portion 31 isformed on semiconductor substrate 30. A dummy layer 32 having side facesis formed on a surface of semiconductor substrate 30 byphotolithography. For example, an silicon nitride film is used as dummylayer 32.

FIG. 38 is a sectional view schematically illustrating a second step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, in the surface of semiconductor substrate 30, a gateinsulating film 33 is formed on a bared portion by photolithography.Gate insulating film 33 is formed so as to come into contact with theside face of dummy layer 32. Next, a gate electrode layer 34 a is formedon a surface of dummy layer 32 and a surface of gate insulating film 33.An auxiliary film 35 is formed on a surface of gate electrode layer 34a. Auxiliary film 35 formed herein has an etching rate slower than thatof gate electrode layer 34 a. Next, as shown by an arrow 57, anisotropicetching is performed on gate electrode layer 34 a and auxiliary film 35.

FIG. 39 is a sectional view schematically illustrating a third step inthe manufacturing method of the semiconductor device according to thisembodiment. More specifically, FIG. 39 illustrates a state aftercompletion of anisotropic etching. Gate electrode layer 34 a provided ona top face of dummy layer 32 is removed. In the surface of gateinsulating film 33, a portion other than a portion in which gateelectrode layer 34 a extends in a vertical direction is removed. Inother words, gate electrode layer 34 a corresponding to a portion cominginto contact with the side face of dummy layer 32 is remained. Thus, agate electrode 34 is formed. Gate electrode 34 has a top face in which asubstantially center portion is recessed in a width direction. Next,auxiliary film 35 remained on the side face of gate electrode 34 isremoved.

FIG. 40 is a sectional view schematically illustrating a fourth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, dummy layer 32 is removed. Further, in gate insulatingfilm 33, a portion other than a portion having gate electrode 34 formedthereon is removed.

FIG. 41 is a sectional view schematically illustrating a fifth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, ion implantation is performed to form an extensiondiffusion layer 36 in a self aligned manner. Herein, extension diffusionlayer 36 is formed on the surface of semiconductor substrate 30 so as toextend from a bottom side of gate electrode 34 toward an outer side.

FIG. 42 is a sectional view schematically illustrating a sixth step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a sidewall insulating film 37 is formed on a side faceof gate electrode 34 and a side face of gate insulating film 33. Next,as shown by an arrow 58, ion implantation is performed to form adiffusion layer 38 in a self aligned manner.

FIG. 43 is a sectional view schematically illustrating a seventh step inthe manufacturing method of the semiconductor device according to thisembodiment. Next, a silicide film 39 b is formed beside sidewallinsulating film 37 on the surface of semiconductor substrate 30. Herein,a silicide film 39 a is formed on a top face of gate electrode 34. Thus,a MOS transistor can be formed on the surface of the semiconductorsubstrate.

The semiconductor device according to this embodiment and themanufacturing method thereof have the following advantage. That is, anauxiliary film is formed on a top face of a gate electrode layer andanisotropic etching is performed; thus, a semiconductor device having agate electrode formed with excellent dimensional accuracy can bemanufactured. In a manufacturing process of the semiconductor device,further, a process margin is improved.

The other actions and effects are similar to those in the first to thirdembodiments; therefore, specific description thereof will not berepeated here.

In the aforementioned drawings, identical or corresponding portions aredenoted by identical symbols. In the aforementioned description, theterms such as “top side” and “bottom side” do not represent an absoluteup and down direction in a normal direction, but relatively representpositional relations of the respective portions.

According to the present invention, it is possible to provide a finesemiconductor device, and a manufacturing method thereof.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1-11. (canceled)
 12. A semiconductor device comprising: a gate electrodeprovided above a surface of a semiconductor substrate with a firstinsulating film interposed between said gate electrode and saidsemiconductor substrate; and sidewall insulating films formed on bothleft and right sides of said gate electrode in a sectional shape,wherein said gate electrode is formed such that left and right surfacesfacing to said sidewall insulating films are substantially parallel witheach other in the sectional shape thereof, and said gate electrode isformed such that a top face is recessed in the sectional shape thereof.13. The semiconductor device according to claim 12, wherein said gateelectrode is formed such that a substantially center portion of said topface is recessed in a width direction in the sectional shape thereof.